In the art it is known to use sandwich-like constructions comprising a steel plate and a concrete layer. Reference is in this connection made to document DE 1800858, which illustrates a construction where a concrete material is cast on a steel plate member. In this configuration it is not possible to transfer shear forces from the concrete to the steel since the bond between steel and concrete is relatively poor in comparison to the requirements in a situation where it is desirable to transfer shear forces from the concrete to the steel plate member.
According to British Standard BS8110, part 1, section 5.4, it is a requirement that when casting concrete on a steel plate, as for example illustrated above with reference to DE 1800858, studs or anchors shall be arranged projecting from the steel into the concrete mass in order to transfer shear forces and thereby activate the steel member. The detailed arrangement, i.e. the size and number of studs/anchors, depends on the actual construction.
The advantages of constructions like the ones known in the art and as claimed by the present invention is that they utilise the good tension probabilities of the steel in combination with the compression capability of the concrete layer. The main problem for the prior art constructions is the transferral of forces from the composite layer, which in the art as mentioned above is a concrete layer to the tension layer in the shape of a steel plate.
According to common practise this is usually done by welding studs onto the side of the steel plate which is to come into contact with the composite layer such that these studs will be embedded in the composite material, preferably the concrete, such that the transferral of forces, especially shear forces which will arise when the construction is exposed to a bending moment, will be transferred to the steel plate via the welded studs.
A number of disadvantages are connected with this. First of all, it is a labour intensive process to weld a sufficient number of studs in order to be able to transfer sufficient force from the concrete layer to the steel plate or vice versa. As the cost of labour is increasing, these types of constructions become increasingly expensive and are un-competitive. Furthermore, in the places where the studs are welded on, the steel plate will, due to the welding process, have different properties than normal steel plates. One of the side effects of the welding process can be that the steel plate is more prone to corrosion in these areas such that especially careful corrosion protection is needed.
An additional problem arises due to the shrinkage of the composite material, for example concrete, during the hardening process. As the concrete shrinks, cracks will appear in the concrete surface. When they appear in such a degree that the concrete layer is not entirely homogenous, the studs will act as crack inducers in the concrete layer. Hereby water, chlorides CO2 and other corrosive elements will gain access to the core of the construction and may cause accelerated corrosion of the construction. It is, therefore, often necessary in order to provide a longer life expectancy for this type of constructions to apply a coating on top of the concrete layer in order to hamper the ingression of chlorides, water and the like.
In order to minimize and distribute the crack formation, the concrete layers in this type of constructions are sometimes reinforced such that a crack distribution is achieved, whereby a smaller crack width, but more cracks, will be generated.
These sandwich plate-like constructions are often used in harsh environments where they may be exposed to dynamic forces which can exaggerate the crack formation and thereby lower the strength of the sandwich construction as well as the expected life span of such a construction. These types of constructions are often found on bridges, ship decks, oil platforms or other similar constructions.